Auto create ApiLocalScope before calling native functions, this ensures that

runtime/vm/code_descriptors_test.cc

Index: runtime/vm/code_descriptors_test.cc
===================================================================
--- runtime/vm/code_descriptors_test.cc	(revision 25778)
+++ runtime/vm/code_descriptors_test.cc	(working copy)
@@ -182,7 +182,6 @@
 
 
 static void NativeFunc(Dart_NativeArguments args) {
-  Dart_EnterScope();
   Dart_Handle i = Dart_GetNativeArgument(args, 0);
   Dart_Handle k = Dart_GetNativeArgument(args, 1);
   int64_t value = -1;
@@ -191,7 +190,6 @@
   EXPECT_VALID(Dart_IntegerToInt64(k, &value));
   EXPECT_EQ(20, value);
   Isolate::Current()->heap()->CollectAllGarbage();
-  Dart_ExitScope();
 }
 
 
@@ -283,4 +281,3 @@
 }
 
 }  // namespace dart
-